As per the statement from problem statement:
'The following image from the visualizer displays the ground truth labeling of a small portion of a single Z-slice. In this image, the bright green marks correspond to label 2, which means the crack is ambiguous. All other colors in this image correspond to unique crack labels.'
Why junctions/crossing of cracks are labelled with 2?
If I assume that X junction is ambiguous what about other kind of junctions, like T junction. From Heuristics examples T junction (and related) should not have label 2.